Electrical resistors – Mechanically variable – Resistance value varied by removing or adding material
Reexamination Certificate
2000-05-30
2001-05-08
Easthom, Karl D. (Department: 2832)
Electrical resistors
Mechanically variable
Resistance value varied by removing or adding material
C338S320000, C338S295000
Reexamination Certificate
active
06229428
ABSTRACT:
BACKGROUND
A resistor is a component of an electric circuit that produces heat while offering opposition, or resistance, to the flow of electricity. A resistor can introduce resistance into an electric circuit. Resistors are primarily used for protection, operation or current control.
In today's high technology electronic environment there is a need to fit a large number of resistors in a narrow space. A large resistor can cause a form-factor problem, especially in a Digital-to Analog Converter (DAC) which is part of an Analog-to-Digital Converter (ADC) Hybrid. The resistor used must be a highly linear resistor as it may be used in converting voltage drive to a current. The linearity requirement places trimming requirements on conventionally fabricated resistors such that the resistor size would adversely affect the form factor of the ADC. Achieving the form factor is critical so that the system resources are not stressed. Most resistors or resistor stacks do not combine a small cross section area and high resolution. To provide higher resolution trims, it is usually necessary to use wider resistors.
For the foregoing reasons, there is a need for a microcircuit resistor stack that fits in a narrow space and can be inexpensively manufactured. Information relevant to attempts to address these problems can be found in U.S. Pat. Nos. 5,196,822, 5,245,145, 6,005,474, and 6,007,755 (None of these patents are admitted to be prior art with respect to the present invention.) However, each of these references suffers from one of the above listed disadvantages.
SUMMARY
The instant invention is directed toward a microcircuit resistor stack that satisfies the needs enumerated above and below.
The object of the present invention is to provide a microcircuit resistor stack, which comprises of a set of equal value resistors connected in series providing a coarse trim, and a wirebond configuration being able to provide the fine resolution trim of the resistor stack. The resistors and wirebond configuration are electrically connected.
The present invention is directed to a microcircuit resistor stack that is a variable value resistor which can be used in hybrid microcircuits where active (laser) trimming is necessary to meet circuit requirements. (Lasers can be used for small scale cutting and welding. They can trim resistors to exact values by removing material within integrated arrays of microcircuit elements.)
It is also an object of the present invention to provide a microcircuit resistor stack that can be configured for high resolution active trimming.
It is also an object of the invention to provide a microcircuit resistor stack that allows a large number of resistors to fit in a narrow space because of narrow resistor width. The microcircuit resistor stack translates a part of the resistor width in the direction of its length.
It is an object of the present invention to provide a hybrid thin film substrate resistor network where each resistor stack has a set of equal value resistors connected in series. Using wirebonds, the value of the resistor stack can be changed. Furthermore if the resistors are over trimmed, second (and third, fourth . . . ) chance resistors are available. Also a less sensitive resistor (higher resolution) can be configured for laser trimming.
It is an object of the invention to provide a microcircuit resistor stack that has a small cross sectional area and high resolution. The microcircuit resistor stack can be compact with very high resolution sections. For hybrid microcircuit high resolution resistor trim applications, multiple microcircuit resistor stacks can be created on a thin film resistor network where space is limited. The microcircuit resistor stack can be used on a high resolution DAC IC circuit. The microcircuit resistor stack is an ideal trim resistor configuration for highly linear DACs.
The present invention provides uniform resistor and conductor dimensions which help the resistor stacks track over temperature. The large variant section can be combined with a high resolution section.
These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims.
REFERENCES:
patent: 3512115 (1970-05-01), Solow
patent: 4146867 (1979-03-01), Blangeard et al.
patent: 4146957 (1979-04-01), Toenshoff
patent: 4242660 (1980-12-01), Cocca
patent: 4298856 (1981-11-01), Schuchardt
patent: 4584553 (1986-04-01), Tokura et al.
patent: 5065221 (1991-11-01), Imamura
patent: 5196822 (1993-03-01), Galluser et al.
patent: 5245145 (1993-09-01), Freeman et al.
patent: 6005474 (1999-12-01), Takeuchi et al.
patent: 6007755 (1999-12-01), Hoshii et al.
patent: 6097276 (2000-08-01), VanDenBroek et al.
patent: 2039920 (1972-02-01), None
patent: 55-44745 (1980-03-01), None
Hoffman, “Quick Trim Aspect Ratio Resistor”, V22, No. 5, p1805 (Oct. 1979).*
“Additive Trim of Polymer Thick Film Resistors”, V30, No. 4, pp 1571-73 (Sep. 1987).
Easthom Karl D.
Glut Mark O.
The United States of America as represented by the Secretary of
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